Method and apparatus for plastic injection



vApril 9, 1946. 'H. F. M MlLLlN ET AL 1 METHOD AND APPARATUS FOR PLASTICINJECTION Filed June 12, 1943 SOURCE OF I20 HIGH FREQUEKY INVENTOR mamfiL m in; MMAJO own b m a m J ATTORNEYS Patented Apr. 9, 1946 METHOD ANDAPPARATUS FOR PLASTIC INJECTION Howard F. MacMillin, Walter Ernst, andGeorge A. Waldie, Mount Gilead, Ohio, asslgnors to The HydraulicDevelopment Corp., Inc., Wilmington, Del., a corporation of DelawareApplication June 12,1943, Serial No. 490,552

Claims.

This invention relates to a method and apparatus for heating and moldingplastic materials.

An object of the invention is to provide a method and apparatus forheating and molding plastic material wherein a predetermined charge ofplastic material is placed between carrying elements that move thecharge into, a heating zone and subsequently moves the charge into amold and applies pressure upon the plastic material in the mold whereinthe material is cured or set.

Another object of the invention is to provide a method and apparatus forheating and molding plastic material wherein the plastic material isheated within a field of high frequency current to rapidly and uniformlyheat the same throughout the entire cross section thereof when theheating and molding process is carried out in accordance with theforegoing object.

Another object of the invention is to provide a process for heating andmolding plastic material wherein a predetermined charge of plasticmaterial is placed between carrier elements that move the charge ofmaterial into a heating zone to raise the temperature of the materialand place the same in a condition suitable for molding, and wherein thecarrier elements move the complete charge of plastic material into amold through an opening that offers substantially no resistance to themovement of plastic material through the same and thereafter applypressure upon the plastic material to cause the same to conform to theshape of the mold cavity.

Another object of the invention is to provide a method and apparatus forheating and molding thermosetting resins wherein a predetermined chargeof resin is raised to a temperature at which polymerization proceedrapidly and is subsequently transferred into a mold cavity in accordancewith the foregoing objects.

Another object of the invention is to provide an apparatus whereinplastic material is heated and molded that is constructed and arrangedin a manner that a predetermined charge of plastic material ispositioned between a pair of reciprocating plunger so that the charge ofmaterial can be transferred into a heating zone wherein the plasticmaterial is heated to a temperature satisfactory for molding and theplungers then carry the plastic material between the same into a mold sothat at least one of them can apply pressure upon the plastic materialin the mold and force the same to conform with the shape of the moldcavity.

- scription.

apparent from the drawing In the drawing:

Figure 1 is a schematic view of an apparatus, partially in cross sectionfor performing the objects of this invention, and shows the plasticmaterial in a mold with pressure being applied thereon.

Figure 2 is a schematic view of a portion of the apparatus shown inFigure l to illustrate the position of the elements when a fresh chargeof plastic material is being fed between the carrying elements for thesame.

Figure 3 is a schematic view of a portion of the mechanism shown inFigure 1 showing the position of the elements of the apparatus whenplastic material is being heated within a high frequency heating zone.

In this invention the apparatus for heating and molding plastic materialconsists of a heating chamber ID that has an internal bore ll withinwhich the plungers l2 and I3 are adapted to reciprocate. A feed hopperI4 is associated with the heating chamber l0 and has a feed opening I 5Further objects and advantages will become that opens into the internalbore ll of the heating chamber Ill.

The heating chamber I0 is provided with a body of electrical insulatingmaterial I B in which there is imbedded a pair of electrodes l1 and I8positioned on opposite sides of the cylinder bore l I.

The electrodes I1 and I8 are connected to a source of high frequency 20by mean of the conductors -2l and 22, respectively, a control switch 23being provided in the conductor 2| to control the application of highfrequency current to the electrodes l1 and I8. I

The source of high frequency 20 may be any suitable source of radiofrequency power that is capable of producing high frequencies on theorder of 1,500,000 to 10,000,000 cycles, depending upon the material tobe heated and the rapidity of which the materiahwill be heated. Radiofrequency power, or high frequency power has been found to besatisfactory for heating materials that normally are resistant to heattransfer, or heat conduction therethrough, such as wood, plastics andothers. If sufficient power is generated, and the frequency of power issufficiently high, the high frequency current will and the following de-2 between the electrodes is substantially constant,

or uniform, throughout the field. In the case of many'of the poorconductors of electric current such as wood, plastics and others, theresistance to the passage of low frequency current is very high inc'ontradistinction to the low resistance to the passage of electriccurrent by means of the various metals. The voltage that would berequired to cause-a 60 cycle current, for example, to pass through thepoor conductors would be so high as to be out of practicalconsideration. However, if the frequency of the current is increased,the resistance of these materials drop rapidly so that at thefrequencies in the range of what we normally call radio frequencies theresistance to the passage I the material.

Regardless, however, of the theory that is accepted, it is now knownthat the poor conductors of electric current, which are also poorconductors of heat, can be heated by the application of high frequencycurrent to the materials by placing them between the electrodes havingthe high frequency current applied thereto so that the material will bewithin the field of high frequency current.

When the applicant thus speaks of a source of high frequency, he isreferring to such a source of high frequency, and the plastic materialthat is heated within the heating chamber I0 is heated by such radiofrequency. current.

A mold or die member 24 is associated with the heating chamber l0 and isadapted to be moved therewith when the mold 24 is separated from thestationary mold or die 25 to permit ejection of a work piece from the,mold cavity 26 provided by co-operation of the die elements 2 4 and 25.One or more double-acting hydraulic motors 21 are provided for openingand closing the die members 24 and 25 and particularly to move the diemember 24 relative to the die member 25. The hydraulic motor, or motors,is provided with a plunger 28 that engages a bracket 29 extending fromthe mold or die 24. The end f the plunger 28 within the cylinder of thehydraulic motor 21 is provided with a piston in a conventional manner sothat fluid entering the hydraulic motor 21 through the conduits 30 and3| will reciprocate the plunger 28.

The conduits 35 and 3| are connected to supply conduits 32 and 33 thatare connected to a 4-way flow control valve 35 whereby fluid underpressure can be directed into either of the conduits 30 and 3 I.

The flow control valve 35 is more or less of conventional form and isprovided with an inlet conduit 36 that directs pressure fluid from thepump 3'1 into the valve 35 to be distributed to the conduits 32 and 33according to the position of the piston heads 33 and 33 that areconnected to an actuating rod 40 extending beyond the body of the valve35. Return flow conduits 4| and 42 are connected to the control valve 35for returning fluid to the reservoir 43. The pump 31 may be of thevariable delivery constant pressure type, and

be controlled by means of the control element 44 that is responsive tothe pressure in the discharge conduit 25 from the pump 31, a conduit 4-5connecting the control element. 44 to the conduit 33 for this purpose.

The plunger l2, previously mentioned, is operated by a double-actinghydraulic motor 50, the plunger I2 being an extension of the plunger ofthe hydraulic motor 50. Fluid supply conduits 43 and 41 are connected toopposite ends of the hydraulic motor .50 for conducting fluid to themotor in accordance with the setting of the control valve 35, theseconduits 46 and 41 being extensions of the supply conduits 32 and 33that are connected to the control valve 35.

An arm 5| is secured to the plunger |2 in any suitable manner to preventaxial movement of the arm on the plunger l2 but which may permitadjustment of the arm upon the plunger l2, if desired, such means beinga clamp 52 and the bolts 53. The free endof the arm 5| has an enlargedhead 54 that is provided with an internal bore to slidably receive a rod55. The opposite A collar 5| is secured to the rod 55 by means of a setscrew 62 against which the arm 5| is urged by means of a spring 53 thathas one end engaging the head 54 and the opposite end engaging a collar64 that is retained on the rod 55 by means of the set screw 65.

It will thus be seen that the ends 58 and 51 of the plungers l2 and I3,respectively, can be positioned a predetermined distance from each otherby adjusting the collar 6| upon the rod 55 so that when the arm 5|engages the collar 8|, as shown in Figure 2, the ends and 51 of theplungers i2 and I3 will be spaced a predetermined distance apart. Also,it may be seen from the foregoing description that the plunger l2 canmove relative to the plunger l3 when the plunger l3 engages a stop 68whereby the space between the ends of the plungers l2 and i3 will bereduced, as shown'in Figure 1, to compress plastic material within amold in a manner to be hereinafter described.

Operation In order to describe the operation of the machine it will beassumed that the operation begins with the feeding of a fresh charge ofplastic material and that the elements of the, machine are therefore inthe position shown in Figure 2. wherein the plungers l2 and I3 arespaced apart a predetermined distance according to the position of thecollar 6| upon the rod 85, the spring 33 retaining the head 54 of thearm 5| in engagement with the collar 6|. With the machine in thisposition it will be apparent that granular or powdered material from thehopper I4 will fall through the feed opening l5 into the space betweenthe ends 55 and 61 of the plungers l2 and I 3, respectively.

The fluid flow control valve 35'may now be shifted to the position shownin Figure 1 whereby fluid under pressure will be supplied through thevalve 35 to the left-hand end of both hydraulic motors 21 and 50 toadvance the plungers 23 and I2, respectively, connectedtthereto. whenthe position the machine is ready to permit plastic material to enterthe mold cavity 26. However, the movement of the plungers I2 and I3 maybe arrested, in the position shown in Figure 3, a sufiicient length oftime by moving the valve 35 to neutral position to permit the plasticmaterial to remain in the heating zone a sufficient length of time toraise the temperature thereof 'hi'gh' enough to plasticlze the plasticmaterial sufficiently for molding purposes. Also, in place of arrestingthe movement of the plungers I2 and I3 they may be moved sufficientlyslowly that the plastic material will be heated during its progress Ithrough the heating zone. However, it is preferable to arrest themovement of the plungers I2 and I3 because an accurate control'over the.temperature rise of the plastic material can thus be obtained in viewof the fact that the intensity of the-heating effect of the highfreque'ncyfield will be known. It is, of course, understood that ifdesired automatic controls can be provided for I operating the valve toregulate the interval of time during which the .plungers I2 and I3 arearrested.

The flow control valve 35 is again shifted into the position shown inFigure 1, thereby causing pressure fluid to be supplied to the left-handend of the hydraulic motors?! and 50. Since the mold member 24 is closedupon the mold mem- -ber 25 there will be no actuation of the hydrauliccavity, whereby all of the heated material will be removed from the moldwhen the formed article is ejected.

After the plastic material has set, or cured, within the mold cavity 26,the flow control valve 35 will be shifted in a rightward directionwhereby the pump discharge conduit 38 will communicate with the conduit33 and the conduit 32 will communicate with the conduit 4| so thatpressure fluid can be delivered to the right-hand ends of the hydraulicmotors 21 and 50. When the plunger I2 compressed the plastic materialinto the mold cavity 26, the arm 5| compressed the spring 63, asillustrated in Figure 1, it being recalled that the head 54 is alsosli'dable upon the rod 55 to permit movement of the plunger I2 when therod 55 was stationary.

With, fluidbeing supplied to the right-hand end of the hydraulic motors21 and" 50, the plungers 28. and I2 move in a leftward direction sothatthe mold member 24 moves in a leftward direction away from the moldmember 25, thereby opening.v the mold. When the plunger I 2 has moved ina leftward direction a suflicient distance that the head 54 on thearm 5Iengages the collar '6I, the plunger I3 will then be' moved by the rod 55and the arm 51 to eject the formed article Thereafter, the

from the fold member 25. plungers I2 and I3 will be in a predeterminedspaced relationship, as illustrated in Figure.2,

and will move in this relationship untilxthe.

plunger I2 has the end 66 thereof adjacent the rear wall of thefeerlopening is, as shown in Figure 2. At this position the hydraulicmotor 50 will stop movement of theplungers I2 and I3, this functionbeing accomplished either manually by shifting the valve 35 to,neutralposition, or it can be accomplished automatically by means of a suitablecontrol mechanism that may be actumotor 21. The pressure fluid suppliedto the hydraulic motor 50 will cause both plungers I2 and 13 to move ina rightward direction, and since the fullflow of the pump 31 is directedto the hydraulic motor 50, the plungers I2 and I3 will be moved at arapid rate. The plunger I3 will move in a rightward direction until itstrikes the stop 68 whereby the end 61 of the plunger I 3 is flushedwith the wall 69 of the cavity 26 so that the end wall of the plungerforms a part of the wall 69. The plunger I2 will continue to advancewhereby the heated plastic material that is carried between the plungersI3 and I2 will be forced into the mold cavity 26 and pressure appliedthereon by the plunger I2 so as to force the material into conformitywith the shape of the cavity. The plunger I2 will retain pressure uponthe plastic material in the cavity 26 until it has set or cured.

From the foregoing description it will be noted that the plungers I2 andI3 reciprocate within the mold in the internal bores 10 and II,respectively, that are of the same diameter as the cylinder bore II, theplunger I3 extending completely through both mold elements 24 and 25when a fresh charge of plastic material is to be picked up by theplungers, as shown in Figure 2. By providing a mold opening ill of thesame size as the heating cylinder bore II, the heated plastic materialmay be transferred from the heating zone into the mold cavity 26 at anextremely rapid rate, and since the end of the plunger I2 can enter thebore I0, all of the plastic material that is heated within the heatingchamber, or

ated by a limit switch at the end of travel of the plunger I2 to operatethe valve 35. r

I The'operation of the machine herein described is particularlyadvantageous when molding thermosetting resins because apredeterminedcharge of a thermosetting resin can-.be placed between the plungers I2and I3 and subsequently advanced into the heating zone wherein thematerial will be raised to a temperature at which it is satisfactory formolding, and at which polymeriza tion of the material proceeds rapidly.Since the entire charge of heated plastic material, in this case,thermosetting resin, may be transferred into the mold cavity 26 at anextremely rapid rate, the thermosetting resin will not have anopportunity to completely cure before the entire charge of resin hasbeen transferred into the mold cavity and pressure applied thereon toforce the same into conformity with the shape of the mold cavity. Itwill be apparent that when the entire charge of plastic material isplaced within the mold cavity, and any excess that remains in theopening 10 will be cured along with the main portion of the formedarticle. All of the thermosetting resin that was heated will be removedfrom the heating chamber upon each cycle of operation of the machine.The method and apparatus herein described therefore provide an injectionmolding machine wherein thermosetting resin can be heated and molded inan intermediate but regular cycle of operation, and there will be nothermosetting resin within the heating or injection cylinder that willpolymerize, or cure, and thus prevent subsequent operation of themachine.

While the process of heating and molding plaszone, will be transferredinto a part of the mold '15 tic material, and the apparatus illustratedto Patent is:

1. An apparatus for heating and molding plastic material that includes,an injection cylinder having a cylinder bore to receive plasticmaterial,

a body of electrical insulating material in said cylinder bore having abore therethrough of the same size as the cylinder bore whereby topermit an injection plunger to traverse both bores, electrode platesembedded in said body of electrical insulating material on oppositesides of the bore through the same and adapted to be connected to asource of high frequenc whereby to form a heating chamber, an opening insaid injection cylinder through which material can be fed into thechamber, a mold associated with the chamber, a co-operating pair ofplunger means reciprocable through said heating chamber including meansinterconnecting said plunger means to dispose them in spacedrelationship whereby a charge of plastic material can be receivedtherebetween, and an actuating mechanism for concomitantly moving saidplunger means in their spaced relationship into operative associationwith said opening to place a charge of plastic material therebetween andthrough the heating chamber for depositing the charge of plasticmaterial in the mold.

2. An apparatus for heating and'molding plastic material that includes,an injection cylinderhaving a cylinder bore to receive plastic materiala body .of electrical insulating material in said cylinder bore having abore therethrough of the same size as the cylinder bore whereby topermit an injection plunger to traverse both bores, electrode platesembedded in said body of electrical insulating material on oppositesides of the bore through the same and adapted to be connected to asource of high frequency whereby to form a heating chamber, an openingin said injection cylinder through which material can be fed into thechamber, a mold associated with the chamber, a co-operating pair ofplunger means reciprocable through said heating chamber including meansinterconnecting said plunger means to dispose them in spacedrelationship whereby a charge of plastic material can be receivedtherebetween, an actuating mechanism for concomitantly moving saidplunger means in their spaced relationship into operative associationwith said opening to place a charge of plastic material therebetween andthrough the heating chamber for depositing the charge of plasticmaterial in the mold, means for arresting the movement of aaeaaie one ofsaid plunger means, said actuating mechanism continuing the advance ofthe other of said plunger means toward the arrested plunger means toplace the plastic material therebetween under pressure in the mold.

3. The process of heating and molding a thermosetting resin thatincludes, placing a predetermined charge of resin within an injectioncylinder and between spaced. carrier members adapted to move the resinthrough a heating zone of high frequency energy established within theinjection cylinder and into a mold, moving the carrier members togetherwith the resin therebetween into said heating zone, arresting themovement of the carrier members to position the 1 resin within the highfrequency heating zone for a sufficient time to raise the temperaturethereof to a point at which polymerization of the resin proceedsrapidly, and again moving the carrier members together with the heatedcharge of resin therebetween into a mold through an opening I thatoffers substantially no resistance to the movement of the resin wherebyto place the. resin within the mold at an extremely rapid rate beforepolymerization is complete.

4. The process of heating and molding plastic material that includes,placing a charge of plastic a material within an injection cylinder andbetween carrier members adapted to move the samethrough a heating zoneof high frequency energy established within the injection cylinder andinto a mold, moving the carrier members together with the plasticmaterial therebetween into said heating zone whereby to heat the plasticmaterial to a temperature suitable for molding, and moving the carriermembers for transferring the heated plastic material therebetween into amold and placing the plastic material in the mold under pressure byreducing the space between the carrier members.

5. The process of heating and molding plastic material that includes,placing a charge of plastic material within an injection cylinder andbetween carrier members that are arranged in spaced relationship forcarrying the plastic material through a heating zone of high frequencyenergy established within the injection cylinder and into a mold, movingthe carrier members to transfer the plastic material into said heatingzone whereby to heat the plastic material to a temperature satisfactoryfor molding, transferring the plastic material between the carriermembers into a mold by concomitant movement of the carrier members, andarresting the movement of one of the carrier members when the plasticmaterial is within the mold to place the plastic material under pressurewithin the mold by continued movement of the other carrier member toreduce the space between the carrier members.

HOWARD F. MACMILLIN. WALTER. ERNST. GEORGE A. WALDIE.

